The mood refers to the emotional tone that is built into a literary text by the author. It helps grasp the readers' attention.
The general mood in the Necklace by of Guy de Maupassant is ironic. It is filled with tense and grim storytelling elements. The given spirit is there from the beginning of the story. It illustrates a high level of the unhappiness of Madame Loisel with her life and her status. It is described through her daydreaming about the luxurious life she was meant to lead. Her actual surroundings are described as ugly and poor, making her suffer greatly.
The mood of "The Necklace" is somewhat wistful, as readers experience Mathilde's desire for all of the things she does not have. There's a certain hopelessness to Mathilde's situation that colors the overall mood of the story, though it's also worth noting that most readers probably recognize the superficiality of Mathilde's materialism. In turn, the story's wistful atmosphere is tempered by the sense that Mathilde is unreasonably preoccupied with appearances and things that ultimately won't bring her happiness.